This invention relates to the field of machine vision, and more specifically to a mechanical apparatus and method for obtaining inspection data for parts in a manufacturing environment. More particularly, the present invention relates to obtaining inspection data for two sides, edges, or surfaces of a part and displaying the same on an imaging device.
There is a widespread need for inspection data for electronic parts in a manufacturing environment. One common inspection method uses a video camera to acquire two-dimensional images of a device-under-test. Current systems have problems. The problems include the inability of getting separated images of portions of the electronic part. To inspect leads on a part, the leads are lighted from the front. One row of leads, solder balls, or pins, for example, along an edge of the part, are lighted from the front and focused on, so that the row of leads on the opposite edge are out of focus thus allowing geometric measurement of the nearby leads. When electrical leads or other shiny surfaces are viewed using front lighting specular reflections result. Portions of the part causing specular reflections generally can not be measured or handled by an optical system.
Elimination of specular reflections requires backlighting of the parts. In current inspection systems, backlighting has a problem since the various features to be viewed are not separated. For example, viewing a first row of leads along an edge also shows another row of leads on an opposite edge. The result is that the information sought, such as co-planarity and other critical parameters may not be accurately obtained since the features behind a critical portion of the object or device under test can not be viewed separately. In other words, the data collected on backlit parts may be bad since another portion of the device under test may introduce error in the measurement of the part.
U.S. Pat. No. 6,141,040 entitled xe2x80x9cMeasurement and Inspection of Leads on Integrated Circuit Packagesxe2x80x9d and issued to Toh discusses an arrangement of optics, cameras and an image processor for capturing images of lead tips of object fields resulting in accurate three dimensional positions of all the leads on a integrated circuit such as a Quad Flat Package (QFP). The system includes a telecentric lens attached to a camera working with an arrangement of mirrors and lighting. The telecentric lens and mirror optical layout splits the acquired image into 2 orthogonal viewing fields of the same lead tips of the QFP. The QFP is placed flat on a pedestal, and for any given side of the QFP, the first field views the lead tips from the front. The second field views the lead tips from the bottom of the IC package. Lead tip images are acquired by a lighting arrangement that casts illumination on the lead tips only. Electronic processing techniques are used to compute the geometry of the leads such as global co-planarity, lead standoff and inspection of other lead defects. This invention only provides views of leads on one side of a package. In addition, the leads are illuminated from the side facing the camera rather than back lighting the leads.
U.S. Pat. No. 6,243,164 entitled xe2x80x9cMethod and System for Determining Co-planarityxe2x80x9d and issued to Baldwin, et al. discloses another system. The co-planarity of leads of an integrated circuit (IC) in a surface-mount technology package (SMT) can be determined by means of a plurality of views without the use of a conventional pedestal, without the use of an associated Z-axis actuator, and without the associated delays required to deploy such a Z-axis actuator. In the invention, three leads of SMT package are arbitrarily selected to define a virtual reference plane in a first or virtual coordinate system, and the positions of the unselected leads are measured with reference to the virtual reference plane. For convenience, the virtual reference plane can be defined as Z=0 and may have height coordinates in Z that are negative or positive with respect to the virtual reference plane. The virtual coordinates are analyzed, and three leads having the lowest Z coordinates are determined to define a virtual sitting plane. For convenience, the virtual sitting plane can be defined as Z=0 in a second or real coordinate system. A mathematical transformation that relates the first coordinate system to the second coordinate system is determined, and the coordinates for each lead of SMT package are subsequently transformed from the first coordinate system to the second coordinate system. In the second coordinate system, each Z coordinate directly corresponds to the lead standoff value that largely determines the acceptability of the inspected SMT package. A variety of techniques are optionally employed to determine whether SMT package is bi-stable.
U.S. Pat. No. 4,959,898 entitled xe2x80x9cSurface Mount Machine with Lead Co-planarity Verifierxe2x80x9d and issued to Landman, et al. discloses an apparatus for performing a non-contact three-dimensional inspection of a surface-mount component prior to placement on a printed circuit board. Specifically, an arrangement to ensure acceptable alignment (i.e. co-planarity) of all component leads in the XZ or YZ plane, where XY is the plane of the component. The apparatus is embodied within a conventional pick and place machine and performs critical, in-process, lead co-planarity inspection. U.S. Pat. No. 4,959,898 also has problems. The views of each of the edges including leads are not separated from one another. There is no divider and therefore there is no separation or blocking off of the view of the leads on the opposite edge of the surface mount component from being shown in a view of the nearby edge.
To overcome the problems stated above as well as other problems, there is a need for an improved machine-vision system that can view sub portions of a device under test using backlighting. There is a further need for a machine vision system that minimizes the problems associated with specular reflections off of shiny surfaces of a device under test. There is a further need for a machine vision system that can accurately measure selected portions of a device under test. There is still a further need for a device that can isolate selected portions of a device under test to assure the accuracy of measurements made on the part. In addition, there is a need for a device that uses a single camera to produce an image with all the desired views. There is also a need for a mechanical system that allows for automated, high-speed, two-dimensional inspection of objects or devices under test.
A machine-vision system for imaging an object having at least a first side, edge or surface, and a second side, edge or surface. The system includes an imager, and an optics apparatus that images two or more views of the first side of the object and images two or more views of the second side of the object. The two or more views of the first side of the object are each from a different angle. The two or more views of the second side of the object are also each from a different angle. The object being viewed includes at least one major surface. The machine vision system also includes a divider background surface that is placed near the at least one major surface of the object. The divider background surface is placed near the major surface of the object in order to obtain separate images of features of the object on the first side of the object and features of the object on the second side of the object. In one embodiment, the divider is opaque.
Another aspect of the invention includes a divider that diffuses light to backlight the features on the object on the first side and backlight the features on the second side of the object. In another embodiment, the divider background surface at or near a major surface of the object in order to obtain separate images of features of the object on the first side of the object and features of the object on the second side of the object. The divider diffuses light to backlight the features of the object on the first side and back light the features on the second side of the object. In some embodiments, the divider includes an elastomeric material. The system optionally also includes a base, and a spring positioned between the divider and base. The spring biases the divider toward the object when at least a portion of the divider contacts the object. The divider includes an edge for contacting the major surface of the object. In some embodiments, the edge of the divider initially forms an angle with respect to the major surface of the object. The divider is biased so that the edge of the divider is substantially in contact with the major surface of the object after initially forming an angle with the major surface of the object. The object is moved both perpendicular to and parallel to the major surface of the object between an initial position and a final position. A picker is used to pick and move objects. On the imager the views of the first side and the second side are within a single image. The machine-vision system also includes a device for measuring dimensions associated with the top view or bottom view (also called the top-down view) of the object. One of the views of the first side and the second side are within a single image on the imager. In one embodiment, a single top-down view of the object shows both the first side and the second side of the object.
Also disclosed is a machine-vision system for inspecting an object. The object has at least a first side and a second side. The machine-vision system includes an imager, and an optics apparatus that images a top down view of the object that includes both the first side and the second side of the object, a separate view of the first side of the object, and a separate view of the second side of the object. In one embodiment, the optics apparatus includes a single camera. The object also includes at least one major surface. The machine vision system further includes a divider background surface placed near or against the at least one major surface of the object. The divider background surface allows the machine vision system to obtain the separate image of the first side of the object and the separate image of the second side of the object. The optics apparatus of the machine vision system further includes a first reflective surface for obtaining the separate view of the first side of the object, and a second reflective surface for obtaining the separate view of the second side of the object. The machine-vision system also includes a base, at least one spring attaching the divider to the base, and a picker for picking and moving objects. The picker moves the object at an angle with respect to an edge of the divider. In one embodiment, a single image includes the top-down view of the object that includes both the first side and the second side of the object, the separate view of the first side of the object, and the separate view of the second side of the object, each of which is backlit. In some embodiments, the machine-vision system includes a measurement apparatus (e.g., a machine-vision computer having image analysis software) for determining dimensions on at least one of the top down view of the object that includes both the first side and the second side of the object, the separate view of the first side of the object, and the separate view of the second side of the object.
Advantageously, the machine-vision system of the present invention can view a device under test using backlighting to minimize or substantially eliminate the problems associated with gathering useful data from images having specular reflections. The machine vision system of the present invention can accurately measure selected portions of a device under test. In addition, the machine vision system of the present invention isolates selected portions of a device under test to assure the accuracy of measurements made on the part. Yet another advantage is that one camera produces an image with all the desired views, including side views of the device under test for checking the co-planarity and a top-down view for checking that the geometry of the device under test will fit a corresponding set of pads on a circuit board. The machine vision system allows automated, high-speed, two-dimensional inspection of objects or devices under test.